1. Field of Invention
The present invention relates generally to air conditioning apparatus, and more particularly, but not by way of limitation, to an improved heat exchanger for use in a heat pump apparatus.
2. Discussion of Prior Art
The heat pump, or reverse cycle air conditioning, has been known for well over a century, having been proposed by Nicholas and Kevin in the nineteenth century. However, it wasn't until after World War II that factory build units become commercially available in this country. Even though the heat pump proved to have superior operating efficiency, not much happened in the way of sales of such units immediately following their introduction, mostly due to the fact that fossil fuels were available in abundance, making energy very inexpensive and operating efficiency relatively unimportant.
These circumstances prevailed until the worldwide energy crisis that developed in 1973, when energy became scarce and the price of energy soared. In response to this, people throughout the world, and especially in this country, began searching for methods to cut consumption and to conserve the amount of energy used to perform heating and air conditioning functions.
Against this background, heat pump economics took on a new and more favorable light, and sales of such units have begun to skyrocket. Some predict that the heat pump will dominate the air conditioning market in the years to come.
The principle of the heat pump is simple, as the heat pump uses a closed loop of refrigerant fluid to move heat from one area to be dissipated at another area. Instead of generating heat, as does the conventional fossil furnace, the heat pump uses energy to move energy, and does its job at about half the operating cost required by conventional air conditioning apparatus.
A typical air to air heat pump apparatus has an outside heat exchanger and an inside heat exchanger. For cooling, a compressor compresses the refrigerant, and by means of precisioned valving, the compressed fluid is passed to either the outside heat exchanger or the inside heat exchanger. In the cooling mode of the heat pump, the refrigerant is first passed through the outside exchanger and then through the inside exchanger. In the heating mode, this is reversed, with the refrigerant first being passed through the inside exchanger and then through the outside exchanger. In effect, during winter months, heat is extracted from the outside air by the refrigerant which is pumped inside to transfer this heat to inside air. In the summer months, heat from room air is picked up by the refrigerant which is pumped outside to transfer the heat to outside air.
Thusly, a water-source heat pump is similar to that which has been described above for an air to air type heat pump apparatus, with the exception that the outside heat exchanger is replaced with a water-refrigerant heat exchange coil that may be located inside. A source of water supplies a stream of water to the water side of the water refrigerant heat coil, and the discharge water is raised or lowered in temperature depending upon whether the heat pump is in the cooling mode or in the heating mode. The other heat exchanger of the water-source heat pump apparatus is the same as the inside heat exchanger of the air to air heat pump apparatus.
For both types of heat pumps discussed above, the inside heat exchanger is required to function alternately as an evaporating coil and as a condensing coil, and the coil must be designed differently than if the heat exchange coil always serves one purpose or the other. For example, fin spacing and face area are different for each of the cooling and heating modes. As a result, the conventional approach has been to compromise these requirements, leading to an optimization that, in theory, would favor neither the cooling or heating mode requirements, but which also would reduce the efficiency of each of the modes. The same considerations, of course, are applicable to the outside heat exchanger of an air to air heat pump apparatus.
In practice, manufacturers have usually favored the cooling mode, and have augmented the heating mode with auxiliary electric heaters. That is, the great majority of prior art units that have been sold in this country have been designed to achieve maximum cooling efficiency; as a consequence, the heating efficiency of such units has been relatively poor. On the other hand, there have been some manufacturers that have favored the heating mode, but their heat pumps have had relatively poor cooling efficiency. Because of these relatively poor heating or cooling efficiencies, a common practice has been to compensate by supplying oversized heat exchangers.
It would be desirable if a heat exchanger could be designed for a heat pump that would afford maximum cooling and heating efficiencies without requiring oversized exchangers to achieve effective cooling and heating performance.